The present invention relates to a new and improved construction of an infrared radiation-burglary detector -- also referred to in the art as an infrared intrusion detector -- of the type comprising radiation-bundling or focusing means and a radiation receiver.
Such detectors serve to detect objects or the entry of intruders or unauthorized individuals, for instance a burglar, into a protected area or room by detecting the infrared radiation emitted by the object or individual. Such radiation can be constituted by the inherent thermal radiation of the object or the individual, for instance in a range between 4 .mu. and 20 .mu., preferably between 7 .mu. and 14 .mu., or there can be provided a radiation source, the radiation of which is reflected by the object or individual to be detected. In the latter case there also can be utilized radiation in the near infrared region, so that there also may be employed components, such as lenses, filters and so forth, which at the far infrared region already exhibit an appreciable radiation absorption.
In order to be able to detect even the slightest movements it has been found to be advantageous to divide the protected room or area into a number of separate receiving regions or fields of view, which are separated from one another by dark zones or fields. If an intruder moves within an area or room protected in this manner, then, it will unavoidably happen that such individual will pass through one or a number of boundaries of the receiving region. At the outlet of the radiation receiver there appear pulse-shaped signals or a signal of varying amplitude. By means of a conventional evaluation circuit these output signals of the radiation receiver can be evaluated for the purpose of delivering an alarm signal.
In the case of prior art infrared radiation-burglary detectors employing a number of separate receiving regions there is generally provided a predetermined pattern of receiving directions, receiving cones or receiving strips. While such detectors can be adjusted into given directions by means of a pivot device or the like, however, there is not possible any individual accommodation and adjustment to individual receiving directions or regions. Therefore, such detectors, generally cannot be accommodated individually to given fields of application.
According to a heretofore known infrared radiation-burglary detector of this type, the different receiving regions are produced by a multiplicity of reflectors which take-up the radiation emanating in each case from one receiving direction and focus the same upon a common radiation receiver. It is conceivable to construct the individual reflectors to be adjustable, however this would require an exceedingly complicated and expensive construction. Additionally, it is necessary to optically correct the individual reflector surfaces depending upon the angle of incidence and angle of reflection, so as to obtain good bundling or focusing, and thus, cleanly separated receiving regions having relatively sharply defined boundaries. The spherical mirrors used with state-of-the-art detectors, at best, are only poorly suitable for this purpose, especially when working with a flat reflection angle. To this end it would be necessary to choose an eccentric section from a paraboloid of revolution, and such section must be chosen with increasingly greater eccentricity the flatter the reflection angle, i.e. for each individual receiving direction there must be selected a different paraboloid-section. With heretofore known detectors employing spherical mirrors or reflectors or centric paraboloid-reflectors the lateral receiving regions, in the case of more pronounced reflection inclination, indistinctively merge with one another at the boundaries. Such prior art detectors, even if the reflectors are constructed to be adjustable, only would be poorly suitable for positively detecting an intruder within a large spatial angular region of a room due to the inadequate optical structure.